RF identification (RFID) systems are well known and the prior art includes different types of RFID systems, different applications for RFID systems, and different data communication protocols for RFID systems. RFID systems are commonly utilized for product tracking, product identification, and inventory control in manufacturing, warehouse, transportation, and retail environments. One type of RFID system includes two primary components: a reader (also known as an interrogator); and a passive tag (also known as a transponder). The tag is a miniature device that is capable of responding, via an air channel, to an RF signal generated by the reader. The tag is configured to generate a reflected RF signal in response to the RF signal emitted from the reader. The reflected RF signal is modulated in a manner that conveys identification data back to the reader. The identification data can then be stored, processed, displayed, or transmitted by the reader as needed.
Another type of RFID system employs active RF tags configured to wirelessly communicate with a reader or wireless access device. In this type of system, an active RF tag includes an integrated power supply, such as a battery, a processor, memory, and an RF radio. The active RF tag periodically broadcasts (chirps) RF signals in an attempt to reach a nearby reader or wireless access device, where the RF signals convey data associated with the respective tag, which in turn is associated with a particular asset, package, item, or product. In practice, an active RF tag may function as a wireless client in a wireless data communication system, such as a wireless local area network (WLAN). In such an environment, the active RF tag can wirelessly communicate with one or more wireless access devices, which may be stand-alone wireless access points or wireless access ports that cooperate with one or more wireless switches located in the WLAN.
Due to their relatively high cost, active RF tags are typically used for tracking and/or locating relatively high valued assets, containers, packages, or items. For such applications, each active RF tag may be assigned a network identifier or address (such as a MAC address), which in turn is associated with a particular asset; the active RF tag is attached to, contained within, or integrated with the asset to enable tracking and locating. A network of wireless access devices in a tracking environment can be used to receive and process the RF signals emitted by the active RF tags. For example, if at least three access devices receive RF signals from one active RF tag, then triangulation techniques and received signal strength measurements can be used to pinpoint the physical location of the active RF tag and, therefore, the associated asset.
Product supply chains often require shipment of assets, containers, and packages on aircraft. Although it may be desirable to track active RF tags as they are loaded on (and unloaded from) an aircraft, aviation rules and regulations may prohibit the transmission of RF signals during takeoff, flight, and landing. Moreover, after an item tagged with an active RF tag has been loaded onto an aircraft for transport, constant monitoring of its location may not be a priority because the item will be inherently constrained within the cargo area of the aircraft. Accordingly, active RF tags should be turned off, powered down, or disabled during certain times while in transit onboard an aircraft. Unfortunately, currently available active RF tags are designed to automatically and continuously transmit (chirp) RF signals until their batteries die. In order to temporarily disable the RF transmit capability of a conventional active RF tag, one would need to remove its battery. Thus, it is impractical to temporarily disable conventional active RF tags onboard an aircraft to address aviation safety regulations.
As mentioned above, active RF tags and other portable wireless devices may rely on battery power. Conventional active RF tags continuously chirp (transmit) until their batteries die. Such continuous chirping wastes battery power in certain situations where transmissions are unnecessary (e.g., overnight or during other idle periods, when the tagged assets are safely stored in a warehouse and are stationary for a known period of time, etc.). Thus, a need exists for a simple and effective technique that can be used to temporarily disable the transmit capability of active RF tags and other wireless devices, which can extend battery life.